In general, a valve timing of an internal combustion engine is determined by valve mechanisms driven by cam shafts according to either a characteristic or a specification of the internal combustion engine. Since a condition of the combustion is changed in response to the rotational speed of the combustion engine, however, it is difficult to obtain an optimum valve timing through the whole rotational range. Therefore, a valve timing control device which is able to change valve timing in response to the condition of the internal combustion engine as an auxiliary mechanism of the valve mechanism has been proposed in recent years.
A conventional device of this kind is disclosed, for example, in Unexamined Japanese Patent Publication (Kokai) No. Hei 9-264110. This device includes a cam shaft rotatably assembled with a cylinder head of an engine, a rotational transmitting member which is driven by the rotational torque from a crank shaft and which is rotatably mounted on the cam shaft so as to surround the rotor, a plurality of chambers which are defined between the rotational transmitting member and the cam shaft, each having a pair of circumferentially opposed walls, a plurality of vanes which are provided with the cam shaft and which extend outwardly therefrom in the radial direction into the chambers so as to divide each of chambers into advancing chambers and delaying chambers, and a coil-spring which is connected with and between the cam shaft and the rotational transmitting member so as to expand the advancing chambers. The coil-spring is located in a depression of the rotational transmitting member. In particular, one end of the coil-spring is affixed to the rotational transmitting member and the other end of the coil-spring is affixed to the cam shaft. The coil-spring includes a coil portion which is disposed in the depression of the rotational transmitting member.
One purpose of locating the coil-spring to expand the advancing chambers is to counteract a delaying direction force to delay the cam shaft, when the engine is driven. The delaying direction force occurs because the fluid chambers and vanes are disposed within a rotating power transmitting passage from the rotational transmitting member to the cam shaft. Therefore, when the cam shaft relatively rotates against the rotational transmitting member in the advancing direction or the delaying direction, the rotation to the advancing side is quicker than the rotation to the delaying side. In the above prior art device, the force of the coil-spring offsets the delaying direction force such that the response of the rotation to the advancing side occurs quickly.
However, the coil portion is not affixed to restrict the radial movement and the axial movement. Rather, both ends of the coil-spring are only affixed to the rotational transmitting member and the cam shaft, respectively. As shown in FIG. 4, an end portion (the first coil) 200a of a coil portion 200 interferes with an inside surface of a depression 201 of the rotational transmitting member, when the cam shaft relatively rotates against the rotational transmitting member to the advancing side or the delaying side. Thus, the friction between the end portion 200a and the inside surface of the depression 201 occurs such that the rotational friction between the rotational transmitting member and the cam shaft is increased. Further, at the inside space of the coil portion 200, if there is a member (although not shown in FIG. 4) which is fixed to a cam shaft, an end portion (the first coil) 200b of the coil portion 200 also interferes with the outer surface of the member such that the rotational friction increases. Therefore, the relative rotation between the rotational transmitting member and the cam shaft is not smooth.